The present disclosure relates to the field of radiography and, in particular, relates to computer tomography (xe2x80x9cCTxe2x80x9d) scanners. Even more particularly, the present disclosure relates to a roller truck for supporting a rotating gantry disk of a CT scanner.
A typical CT scanner includes a gantry comprising an annular frame for rotatably supporting an annular disk about a rotation or scanning axis of the scanner. The disk includes a central opening large enough to receive a patient extending along the scanning axis, and the disk is rotated about the patient during a scanning procedure. An x-ray tube is positioned on the disk diametrically across the central opening from an array of x-ray detectors. As the disk is rotated, the x-ray tube projects a beam of energy, or x-rays, along a scan plane, through the patient, and to the detector array. By rotating the x-ray source about the scanning axis and relative to the patient, x-rays are projected through the patient from many different directions. An image of the scanned portion of the patient can then be constructed from data provided by the detector array using a computer of the scanner.
Because even minor mechanical noise and/or artifacts causing undesirable vibration of the CT scanner during a scan can cause faulty or erroneous image information, the gantry of such a scanner typically has been provided as massively reinforced structures often weighing a ton or more in order to reduce motion due to such mechanical noise and artifacts. Consequently, because of the weight, the massive drum has usually been supported in the frame by an expensive and heavy precision roller bearing or ball bearing assembly.
Many of the disadvantages inherent in such massive, expensive, relatively fixed CT scan structures were recognized and addressed, at least in part, by the apparatus disclosed in U.S. Pat. No. 4,928,283 issued May 22, 1990 to Gordon, and in U.S. Pat. No. 5,109,397 issued Apr. 28, 1992 to Gordon, et al., both of which are assigned to the assignee of the present disclosure. In the aforesaid ""283 patent, the patentee broadly suggests the use of rollers rather than bearings for rotatably supporting the drum in a frame, without however any discussion of the nature and characteristics of such rollers. The simple replacement of bearings with rollers may introduce deviations or wobble as the drum is rotated in its plane, resulting in undesirable inaccuracies in the tomographic image produced. The ""397 patent addresses, inter alia, the use of electromechanical sensors that follow the outer periphery of the disc in the plane of rotation to provide compensating electrical signals for modifying or correcting the data received by the X-ray detection array.
U.S. Pat. No. 5,473,657 issued Dec. 5, 1995 to McKenna, which is assigned to the assignee of the present disclosure, discloses an improved x-ray tomography structure including a frame supporting a rotatable gantry drum. The entire mass of the drum rests upon at least two pairs of resilient rollers so that the top half of the drum is unconstrained (for centerless rotation) so as to allow the drum to freely expand and contract without introducing error-producing stresses into the drum or frame. Each pair of rollers is mounted in an elastically compliant truck, the truck being pivotably supported about a pivot axis disposed between and parallel to the rotational axes of the two rollers supported by the truck. The resilient rollers serve to (a) dampen the transfer of vibrations to the drum as the latter rotates, and (b) accommodate temperature cycling of the drum.
What is desired is a CT scanner gantry including all of the benefits of the McKenna patent, as well as additional benefits.
The present disclosure, accordingly, provides an improved roller truck for supporting a rotating instrument drum of a CT scanner. The roller truck includes a spring plate, and an attachment member and axles secured to the spring plate. The spring plate extends between opposing ends, and includes top and bottom surfaces and unconstrained side edges extending between the opposing ends.
The axles are secured to one of the bottom and the top surfaces of the spring plate, and the attachment member is secured to one of the bottom and the top surfaces of the spring plate, between the two axles, and extends substantially parallel with each axle. The attachment member is for securing the roller truck to one of a support frame of a CT scanner and an instrument drum mounted for rotation on the support frame. Rollers are rotatably mounted on each axle for supporting and allowing the instrument drum to rotate with respect to the support frame of the CT scanner.
The spring plate is free to resiliently bend about the attachment member and is adapted such that, when the instrument drum of the CT scanner is rotated during operation of the CT scanner, the roller truck shifts vibration frequencies associated with the rotating drum away from a resonant frequency of the system. The roller truck thereby reduces distortions in reconstructed images produced by the CT scanner.
These and other features and benefits of the present disclosure will become more apparent upon reading the following specification in conjunction with the accompanying drawing figures.